A variety of different apparatuses exist for mining coal and other materials from underground seams. One apparatus that is commonly used in underground mining operations comprises a mining machine used in instances where extended portions or longwalls of seam are to be mined. Such longwalls may, depending upon the seam configuration, extend for distances of 1200-1500 feet. It is standard practice in this type of mining to mine parallel entries into the seam to be mined and connect those entries with one or more primary passages. This procedure defines the longwall pillar(s) to be mined. The roof of the primary passages is then supported by movable roof supports during the mining of the exposed “face” of the longwall pillar.
Conventional longwall mining techniques employ a mining machine that is known in the industry as a longwall shearer. In alternate arrangements, a plough is used instead of a longwall shearer.
A longwall shearer typically has an elongated mobile frame that is supported on floor-mounted tracks that are adjacent and substantially parallel to the mine face. Rotary driven toothed drums are operably supported on arms on each end of the elongated frame for winning the coal as the frame passes back and forth before the mine face. The won material falls onto a face conveyor that is attached to the floor-mounted tracks and extends parallel to the longwall face. The face conveyor discharges the material onto other conveying apparatuses to transport the material from the seam. As the mine face recedes, the conveyor and track assembly is advanced forward to enable the shearer to continue mining.
FIG. 1 illustrates a conventional longwall system 10 having a mining machine in the form of a shearer 12 (carried on a face conveyor 14) and a cantilevered roof support 16. As the longwall system 10 advances through the panel 18, the self-advancing roof supports 16 advance toward the face 20 in a well-known manner.
More particularly, the cantilevered roof support 16 is a chock roof-engaging beam support unit having a floor-engaging base 42 and a shield 24 supported by two hydraulically operable support legs or rams 28 (only one of which is shown) spaced from the face conveyor to define an access travelling way 30. A roof-engaging beam 32 is pivotally attached at 34, to the shield 24 and the shield 24 is connected by cantilevered linkage 40 to the base 42. The roof-engaging beam 32 also carries at its front end a face sprag assembly 48 including a contact plate 50 that is shown in a face-supporting mode, where the plate 50 is extended from its stowed position by a hydraulic cylinder 54 to a position where it abuts a part of the face. The face sprag assembly's fully extended position is shown in ghost in FIG. 1.
The shearer 12 has a mining machine support in the form of an elongated mobile frame 60 with a skid-type shoe 64 that is movably supported on a race 68 that is substantially parallel with the longwall face. A laterally extending rotary drum 70 which has a plurality of mining bits 74 attached thereto is pivotally attached to each end of the elongated mobile frame 60 by a corresponding boom member 78. The operation of the shearer 12 is well known in the mining art and, as such, will not be discussed in detail herein. However, the skilled artisan will appreciate that the shearer 12 is moved back and forth on the race 68 such that the mining bits 74 on the rotating drums 70 can be brought into engagement with the mine face to dislodge material there from. As the face recedes, the race 68 and shearer 12 are advanced towards the face to enable the mining process to be continued.
In some mining operations, as shown in FIG. 2, a longwall operation includes an armored face conveyor 100 in front of the roof supports 104, and an armored face conveyor 108 behind the roof supports 104. The armored face conveyor 108 behind the roof supports 104 collects coal falling from above the roof supports, as the roof supports 104 advance. This form of mining is known as top coal or sub level caving. The tailgate roof support 104 used in such an operation includes a floor-engaging base 112, a pair of support legs 116 supporting a middle roof-engaging beam 118, a forward roof-engaging beam 120 pivotally connected to the middle roof-engaging beam 116, and a two-piece rearward roof-engaging beam 124 supported by another pair of support legs 128. The two-piece roof-engaging beam 124 at the rear of the roof support 104 covers the armored face conveyor 108 behind the roof support 104.
At the roadway or main gate end of the longwall, an extra wide and extra long roof support assembly 129 is required, and is illustrated in FIG. 3. The roof support assembly 129 includes two spaced apart roof supports 130. Each main gate end roof support 130 includes a rearward floor-engaging base or pontoon 134, a forward floor-engaging base or pontoon 138, and spaced apart support legs 142 are connected between each of the pontoons 134 and 138 and a respective roof-engaging beam 146 and 150. The rearward pontoon 138 also includes a shield 152 pivotally connected to the roof-engaging beam 146, and linkage 154 connects the shield 152 to the rearward pontoon 134. The forward pontoon 138 also includes a shield 158 pivotally connected to the roof-engaging beam 150, and linkage 164 connects the shield 158 to the forward pontoon 138. In other words, the main gate roof support 130 includes a forward facing roof support at one end, and a rearward facing roof support at the other end, with the two supports joined in the middle at 159. At the point of adjoining, each roof support carries a ram 168 and 172 that extends up to the respective roof support roof-engaging beam.
To assist in supporting the roof, each of the two roof supports 130 also include spaced apart middle plates 176 that extend between the two adjacent roof supports 130, creating an overlap. The overlapping middle plates 176 are not connected. The two adjacent roof supports 130 are used because each roof support has its own pontoons, for the floor of the mine is irregular as the roof support 130 advances. The pontoon of each roof support needs to be able to move vertically independently of the adjacent pontoon. Because the adjacent roof supports are not connected, it is difficult to maintain, as the roof support assembly 129 advances, the same roof support adjacent positions.
In the above-described typical top coal caving longwall mining operation, there are two drilling entries and a wall face across between the entries, with mining then being backwards along the entries. In a different form of mining, illustrated in FIGS. 4A and 4B, known as an advancing longwall system, the entire mining operation moves forward into the coal face. Only a single forward conveyor is used in such a system. A roadway 180, known as a gate road end, supporting the mining operation, needs to be cut and maintained separate from the longwall face. Construction of the gate road end adds complexity to the overall mining operation. When the gate road end 180 is being cut, a wall 184 has to be made to prevent the falling roof from entering the roadway. The difficulty of creating and supporting such a wall is significant. In order to reduce the amount of goaf pressure bearing against the man-made wall 184, fully roof-engaging beamed buttress supports 188 are provided at the gate road end 180 to reduce the goaf pressure on the man made wall 184.